I've just read James Allen's book, «As You Think» (free download). Eventually, one of the master pieces of self-development literature. This book was wrote in 1904 and has within it the whole principles of the effects that thoughts have in our lives. Which means in our character, in our circumstances, in our health, in our goals, purposes, vision and ideals.
Actually, we do, we are, we achieve and we live simply what we think. If you manage to recognize that you can change everything around you, you will really. We can control much of our feedback. Here you are some phrases of this small but great book:
«Thoughts of doubt and fear never accomplished anything, and never can. They always lead do failure. Purpose, energy, power to do, and all strong thoughts cease when doubt and fear creep in» (...)
«Doubt and fear are the great enemies of knowledge, and those who encourage them, who do not slay them, thwart themselves at every step»
«Stronger people cannot help the weaker unless the weaker are willing to be helped»
«The thoughtless, the ignorant, and the lazy, seeing only the apparent effects of things and not the things themselves, talk of luck, of fortune, and chance.»
«We cannot directly choose our circumstances, but we can choose our thoughts, and so indirectly, yet surely, shape our circumstances»
Of course the small book is not confined to those phrases, there are a lot more. I really advise you to read it.